iPad Air 5th gen iPadOS 18.6.2 256Gb build 1937
While playing a long song (9:45 in my example] with timecoded lyrics and highlight position in autoscroll set to top (although the fault still happens with centred) the highlighted verses are progressively displayed lower down the screen as the song plays until eventually the highlighted text is not displayed on the screen at all.
On another longer song (of 23:23 length) the opposite happens where the highlighted lyrics appear higher each time until they are off the screen above.
Both tracks work perfectly on ST3